1973 年 38 巻 4 号 p. 615-621
The effects of ionizing radiations (X- and gamma rays) and chemical mutagens (EMS and DES) on chromosome association and chiasma frequency were studied in the M1 plants of Sorghum purpureosericeum (2n=10) raised from the treated seeds in comparison with control. Of the treatments, radiations induced a high frequency of translocations as well as univalents compared to the treatments with chemical mutagens. The frequency of translocations showed an increase at higher doses of radiation treatments. There was, in general a decrease in the frequency of chiasmata in the treated plants compared to the control plants excepting 9.70 mM EMS. Radiation treatments caused more decrease in the chiasma frequency as compared to the treatments with chemical mutagens. In contrast to the reduction in the number of bivalents with three chiasmata per bivalent, the number of bivalents with single chiasma increased in the treated plants when compared to the control plants. The mechanisms of forming chiasmata are discussed in the light of present investigation.